Much of early speech and language development is actually non-verbal. One of the first ways an infant communicates with a parent is through eye contact. As early as at 6 to 8 weeks, a tot should be able to hold a gaze—particularly with a parent or other caregiver. Around that age, a child should also have a social smile in response to a parent or loved one.

2. A child isn’t using gestures.

Also in the category of non-verbal communication, an infant should begin using gestures by the time he or she is between 6 to 12 months. These include clapping, pointing and waving.

3. A child isn’t cooing or babbling.

Well before the long-anticipated first word is spoken, a child should be verbalizing in sounds. Cooing typically occurs by the time a child is 2 to 4 months old, and babbling by 6 months. I have heard parents say, “He was such a good baby, he was so quiet.” That is a red flag for me. By age 1, a child generally should say 1 or 2 words. By age 2, a child should be stringing 2 or more words together.

4. A child is not understood by others.

Parents are wonderfully attuned to their children’s needs. They can sense subtle differences in their cries of needing to be changed, or being hungry, tired or in pain. As the months progress, parents get even better at deciphering what their child wants. But even if they understand a child’s sounds or words, they should pay close attention to whether other people can understand what their child says. If others cannot understand a child by 18 months to 2 years, this is an indicator of a potential speech or language issue.

5. A child is not responding to his own name.

This can be a sign of hearing impairment. Parents may not realize the need for vigilance about hearing because most newborns undergo hearing screening before leaving the hospital. However, hearing problems can emerge weeks or months following birth. Ear infections can also lead to hearing problems. Hearing issues may not be obvious, especially given that a child with a hearing impairment will make similar sounds (including cries) to a non- hearing-impaired child through 9 months. If a child is not responding to his or her own name by 7 months to a year, a problem may exist.

Taken from: http://www.parents.com/blogs/to-the-max/2013/10/17/autism/5-signs-of-communication-disorders-parents-often-miss/?